Invert emulsion fluids, i.e. emulsions in which the aqueous fluid is the discontinuous phase and the oil fluid is the continuous phase, are employed in drilling processes for the development of oil or gas sources, as well as, in geothermal drilling, water drilling, geological survey drilling and mine drilling. Specifically, the invert emulsion fluids are conventionally utilized for such purposes as providing stability to the drilled hole, forming a thin filter cake, lubricating the drilling bore and the downhole area and assembly, and penetrating salt beds without sloughing or enlargement of the drilled hole.
Oil-based drilling fluids are generally used in the form of invert emulsion muds. An invert emulsion mud consists of three-phases: an oil phase, an aqueous phase and a finely divided particle phase. The percentage distribution of water and oil in the liquid phase can range from 50% oil:50% water to 95%:5%, although most invert emulsion muds range from 75:25 to 90:10. Also typically included are emulsifiers and emulsifier systems, weighting agents, fluid loss additives, viscosity regulators and the like, for stabilizing the system as a whole and for establishing the desired performance properties. Full particulars can be found, for example, in the Article by P. A. Boyd et al. entitled “New Base Oil Used in Low-Toxicity Oil Muds” in the Journal of Petroleum Technology, 1985, 137 to 142 and in the Article by R. B. Bennet entitled “New Drilling Fluid Technology-Mineral Oil Mud” in Journal of Petroleum Technology, 1984, 975 to 981 and the literature cited therein.
During the drilling process, it is not uncommon for the drilling fluid to encounter a water-bearing formation and thus the ratio of oil fluid to aqueous fluid is less than optimal. In some cases, the oil water ratio becomes so out of balance that the mud becomes too thick to use, creating ting a difficult-to-break emulsion. This out-of-balance mixture of drilling fluid and water is often referred to as the “slop”. The oil to water ratio in the slop may be 25/75 or 30/70 or similar such numbers. Conventionally, this slop is diluted with make-up oil to achieve the desired ratio, typically 80/20. The large amount of oil required and the resulting large inventory of mud create both storage and opportunity costs.